Free machining corrosion resisting steel



Patented Feb. 23, 1932.

V UNITED STATES PATENT OFFICE FRANK R. PALMER, OF READING, PENNSYLVANIA,ASSIGNOR TO THE CARPENTER STEEL COMPANY, OF READING, PENNSYLVANIA, ACORPORATION OF NEW JERSEY- IREE IACHINING CORROSION BESISTING STEEL EHDrawing.

My invention consist particularly in a new and improved high chromiumcorrosion resisting steel having relatively free machining properties;corrosion, as herein used, c0mprehending attack by chemical reagents andoxidation or surface deterioration at elevated temperatures, and thecorrosion resisting steels to which my invention relates being those inwhich the corrosion resistance has been imparted primarily by theelement chromnnn.

Such steels are well known in the art, containing chromium from 2% to60%, frequently modified by additions of copper, molybdeis num, silicon,tungsten and nickel; the nickel element bein often added in sufficientquantities to pro uce an austenitic non-magnetic steel, and the contentaside from these elements being principally iron with suflici ent carbonto accomplish the purpose desired in each case.

In my co-pendingapplication No. 247,462 for an anti-friction and freemachining corrosion resisting steel, I have fully ointed out how highchromium in steel ren ers the.

products difiicult to machine, and how the deliberate employment ofabnormally high percentages of sulphur overcomes the objec' tionableefi'ect of the chromium without markedly interferin with the corrosionresisting properties. y present invention avoids some of the undesirablefeatures of such high sulphur steel as specifically set forth in saidearlier application; a mam fact being that sulphur is objectionable froma merchandizing standpoint because it has been regarded for many yearsas a harmful ingredient, and that this prejudiceis communicated to someextent to my high chromium corrosion re sisting steels in which commonlyprohibited high percentages of sulphur are deliberately employed. Mypresent invention rovides for producing a free machining r0 not withoutincurring this objection inci ent to high sulphur content.

' Furthermore, as pointed out in my prior application, the sulphurcombines with various metals present in the steel to form metalsul hideswhich are insoluble in the solidifled steel, so that forged or rolledspecimens Application filed December 7, 1929. Serial No. 412,576.

of high sulphur corrosion. resisting steel, when polished and viewedunder a metallurgical microscope, reveal considerable quantities ofelongated slag-like sulphide inclusions which are objectionable in thatthey reduce the ductility and toughness of the I metal in a directionnormal to the direction of rolling or forging; whereas in my presentinvention, free machining qualities are imparted with decidedly lessslag-like inclusions than in the case of hi h sulphur steels,constituting a very desiraile improvement.

In the periodic table of chemical elements, sulphur occurs in a grouphaving a valence of 2 with hydrogen and a valence of 6 with oxygen,usually referred to as grou VI. This group is headed by oxygen whic is agas, and the elements of higher atomic weight than oxygenfall intotwogroups; one group comprising metalloids and the other group comprisingmetals. The metalloid group consists of sulphur, selenium and telluriumwith atomic weights of approximately 32, 79 and 127 respectlvely. Thesethree metalloids are known to be closely related in many of theirproperties and when referred to jointly hereinai'ter will be termedgroup VI metalloids.

I have found that selenium and tellurium have the property, when addedto high chromium corrosion resisting steel, of imparting free machiningproperties in like manner to sulphur, and that they at the same timeavoid the principal objections to sulphur above referred to. There is noeneral prejudice against selenium and tellurium, and their use thereforedoes not interfere with the merchandizing of the product; microscopicexamination of a series of high chromium corrosion resisting steelscontaining various percentages of selenium and tellurium reveals thatthese metalloids, like sulphur, appear to combine with a metal, formingwhat is 'udged to be metal-selenides or metal-tellurides which a pearvery similar to metal-sulphides.

owever, the selenides and tellurides are evidently' more soluble in thesolidified steel than sulphides because a iven percentage of either orboth does not yie (I nearly so much slag-like inclusion as would thesame percentage, of. sulphur. My examinations and tests 1W sults aimedfor.

reveal no notable difference between the behavior of selenium andtellurium insofar as they are used to achieve the objects of thisinvention. They apparently can be variedly used with ordinary judgment,either llldlVldually, or jointly, and with or without sulphur, so as tosatisfactorily achieve the stated re- 1 have further discovered that itis not necessary to use as much selenium or tellurium, singly orjointly, as would be necessary in the case-of sulphur alone to securesatisfactory machining properties. As pointed out in said a plication,No. 247,462 sulphur has little e ect on the machining properties of highchromium corrosion resisting steel, particularly when the chromiumexceeds 10.00%, until the sulphur exceeds .15% by weight of the mass;whereas I have obtained very satisfactory machining properties by usinonl about .07 of selenium or tellurium, t oug I have found the optimumpercentage of these new metalloids to be about .20% by weight. 'So faras I am aware neither selenium nor tellurium have been heretofore usedin any ferrous alloy for the present stated purpose,'or any other.

Hi h hromium corrosion re'sistin steels, as now commonly employed,contain a ut .20 to .50% mangane'se. In my prior a plication No.247,462, I have pointed out t at hot h following type compositions:

malleability may be preserved in high. sulphur corrosionresisting-steels by increasing the manganese percentage above this normarange or by the addition of a metal like zircomum, in order to preventthe formation of a preponderance of iron-sulphide with resultant redshortness. In my present invention,

- since tellurium and 'selemumilsingly or jointly, need not be added insuc large percentages as sulphur, and also presuma ly because 0 theirpartial solubility in the steel base, the need for s ial alloy additionsto secure hot malleabilityis not so vital. Neverthe less, I prefer, 1nthe interests of good steel making practice, to use increased manganeseor a metal like zirconium in conjunction with the metalloids noted. Y

My invention -is fully embodied inhigh chromium corrosion resistingsteels of the Carbon Chromlumfiulphur Zirconium Selenium Tellurium Ihave carefully compared steels of the above type compositions withsteels. of the following type compositions Carbon Chromium SulphurZirconium Selenium Tellurlum Steels (a). and ((1) do not machinesatisfactorily with the usual machine shop practice because the chipstend to all and adhere to the tools, producing a con 'tionfrequentrosion resisting steels containing minor per-' centages of otheralloys such assilicon, copper, molybdenum and tungsten; and with nickeladditions even suflicient to produce an austenitic product, theapplication of my mvention produces markedimprovement in machiningproperties.

Steels within the scope of this invention can readily be made in acrucible pot furnace by compounding the corrosion resisting baseanalysis steel in accordance with usual crucible steel meltin practiceand adding metallic selenium or te lurium or both, just before pouringthe metal fromthe crucible. Both metalloids are quite volatile andshould be added in stick form-rather than as a powder, and losses can bereduced by thrusting the metalloids beneath the surface of the moltensteel on the end of a rod. In any case an excess of metalloid rangingfrom'2 to 10 times the residual quantity requiredshould be allowed forvolatilization, the exact excess necessary varying according to theindividual melters mani ulations in adding the metal loids. Theseimproved free machining steels can also .be made in the electric furnacebut.

the selenium andtellurium should be added in the ladle with dueprovision forloss.

It-is to be understood from the above description, that my presentinvention is a further development of the invention specifical- 1y setforth in my said prior. application 50-, r1al No. 247,462, t beingbased-on determination of the fact that the elements selenium andtellurium, of the recognized periodic group VI, may be used individuallyor jointly to replace wholly or in partthe sulphur of said group, andwith stated advantages over use of sulphur alone as previouslydescribed; the essential desired. effect of free machining bemgapparently always secured,with and incidental to resulting reduction .ofhigh frictional quality in the alloy; and such main desired effect beingsecured-by an actual content in the. alloyof between 03% and 2.00%,

of the group VI metalloids.

WhatI claim is:

1. As a composition of matter an alloy steel containing chromium between4% and 60% and the elements selenium and tellurium of a total percentagebetween .03%' and 2%, and characterized by relatively free machiningquality.

2. As a composition of matter, an alloy I steel containing chromiumbetween 4% and 60% and selenium between 03% and 2%, and

